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Growth, photosynthesis, nitrogen partitioning and responses to CO₂ enrichment in a barley mutant lacking NADH-dependent nitrate reductase activity
- Plant growth, photosynthesis and leaf constituents were examined in the wild-type (WT) and mutant nar1 of barley (Hordeum vulgare L. cv. Steptoe) that contains a defective structural gene encoding NADH-dependent nitrate reductase (NADH-NAR). In controlled environment experiments, total biomass, rates of photosynthesis, stomatal conductance, intercellular CO₂ concentrations and foliar non-structural carbohydrate levels were unchanged or differed slightly in the mutant compared with the WT. Both genotypes displayed accelerated plant growth rates when the CO₂ partial pressure was increased from 36 to 98 Pa. Total NADH-NAR activity was 90% lower in the mutant than in the WT, and this was further decreased by CO₂ enrichment in both genotypes. Inorganic nitrate was greater in the mutant than in the WT, whereas in situ nitrate assimilation by excised leaves was two-fold greater for the WT than for the mutant. Foliar ammonia was 50% lower in the mutant than in the WT under ambient CO₂. Ammonia levels in the WT were decreased by about one-half by CO₂ enrichment, whereas ammonia was unaffected by elevated CO₂ in mutant leaves. Total soluble amino acid concentrations in WT and mutant plants grown in the ambient CO₂ treatment were 30.1 and 28.4 μmol g⁻¹ FW, respectively, when measured at the onset of the light period. Seven of the twelve individual amino acids reported here increased during the first 12 h of light in the ambient CO₂ treatment, leading to a doubling of total soluble amino acids in the WT. The most striking effect of the mutation was to eliminate increases of glutamine, aspartate and alanine during the latter half of the photoperiod in the ambient CO₂ treatment. Growth in elevated CO₂ decreased levels of total soluble amino acids on a diurnal basis in the WT but not in mutant barley leaves. The above results indicated that a defect in NADH-NAR primarily affected nitrogenous leaf constituents in barley. Also, we did not observe synergistic effects of CO₂ enrichment and decreased foliar NADH-NAR activity on most N-containing compounds.
Sicher, Richard C. , Bunce, James A.
Hordeum vulgare , barley , nitrate reductase (NADH) , enzyme activity , mutants , plant growth , biomass , photosynthesis , nitrogen , carbon dioxide , carbohydrates , stomatal conductance , gas exchange , nitrates
- Includes references
- Physiologia plantarum 2008 Sept., v. 134, no. 1
- Oxford, UK : Blackwell Publishing Ltd
Journal Articles, USDA Authors, Peer-Reviewed
- Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.